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Basic Generator Theory
The generator creates electricity by a series of fine wire windings inside
a magnetic field, called an armature. As the armature is spun inside this
magnetic field by the generator's motor,
current and voltage gets generated in those windings of wire and electricity is transferred. That current and voltage will be directly proportional to the speed that the armature spins and to the strength of the magnetic field.
Each complete revolution, one complete cycle of alternating current (AC) is
developed. This is called a rotating armature.
In a stationary armature, the magnetic
field rotates around the armature. The advantage of having a stationary armature
winding is that the generated voltage can be connected directly to the load.
The frequency of the generated voltage is
dependent on the number of field poles and the speed at which the generator is
operated. Frequency, measured in Hertz (Hz), is the number of complete cycles
per second in alternating current direction. As current flows through the
armature, there is some amount of resistance and inductive reactance. The
combination of these make up what is known as the internal resistance..
When the load current flows, a voltage drop is developed. When a Direct Current (DC) voltage is applied to the field windings of a
dc generator, current flows through the windings and sets up a steady magnetic
field. This is called Field Excitation.
An exciter is part of the generator package supplying direct current to the
alternator field windings to magnetize the rotating poles. The exciter output
may be controlled by a voltage regulator. Types of exciters include brush type
with rotating commutator, static excitation or brush less generator and exciter.
A regulator is an important option to consider if there are frequency or voltage
sensitive equipment such as computers.
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